Ser. No. 763,160 discloses and claims a chemical sensor matrix that operates by chemo-electronic means, that has configuration adaptable for the detection of many chemical agents, that is small in size, of light weight, low in cost and that has a high sensitivity of detection. The chemical sensor matrix is comprised of a plurality of bulk acoustic wave (BAW) resonators embedded in a single monolithic piece of piezoelectric crystal. The resonators are arranged in rectangular row and column configuration including m rows and n columns, the (mn) th resonator having nominal frequency f.sub.mn and each of the resonators being separated from its neighboring resonators by distances such that the resonant energies do not overlap. Each of the resonators is provided with etched tunnels that are coated within by a chemical substance particular to that resonator and different from the chemical substance used to coat any other resonator, the chemical substance being sensitive to a chemical agent to be detected so that when the chemical agent reacts with the chemical substance the frequency f.sub.mn changes. Each of said rows of resonators bears a metallic electrode stripe for that row, and each of said columns of resonators bears a metallic electrode stripe for that column. The electrode row stripes are positioned on the top surface of the crystal, and the electrode column stripes are positioned on the bottom surface of the crystal. The areas of overlap of the row and column stripes are registered with the central portions of the embedded resonators. Two diode arrays are positioned on the periphery of the crystal for addressing the individual row electrode stripes and the individual column electrode stripes so that the desired resonator can be activated by connecting the stripe corresponding to its row address and the stripe corresponding to its column address to suitable active oscillator circuitry and signal processing means. The resonators (mn) are then interrogated sequentially and frequency changes registered.
In addition to the etched tunnels coated within by a chemical substance to be sensitive to a chemical agent to be detected, each of the resonators may also be coated on its surface with the chemical substance used to coat within the etched tunnel of that resonator. The two types of coatings acting together can enhance the sensitivity of the resonator to an even greater extent than either coating acting alone.
Although the BAW configuration as disclosed and claimed in Ser. No. 763,160 is adequate, it still lacks the capacity for microwave frequency application. To overcome this problem, one must provide a chemical sensor capable of higher frequency application compatible with modern communications technology and even more sensitive to the effects of mass loading and stress biases.